The Main Reasons for the Aging of ABS Plastic

  ABS plastic undergoes aging in natural environments due to a combination of interacting factors, with oxygen being the primary culprit. While both light and heat significantly accelerate this degradation process, the effect of ultraviolet (UV) light is particularly potent. A common and visible sign of this aging is yellowing. The chemical mechanism behind this yellowing involves the isolated double bonds within the polybutadiene phase of the ABS structure. These double bonds react with oxygen to form hydroperoxides, which subsequently trigger the degradation of the adjacent Styrene-Acrylonitrile (SAN) phase. This chain of reactions leads to the formation of chromophoric groups, such as carbonyls, within the polymer chains, which absorb light and cause the yellow appearance. The energy of light is inversely proportional to its wavelength, meaning shorter-wavelength UV light carries the most energy. When comparing this energy to the dissociation energy of common chemical bonds in polymers, it becomes clear that UV radiation possesses sufficient energy to break these bonds, directly causing the aging and degradation of the polymer material. In summary, environmental oxygen initiates the primary chemical degradation of ABS, while UV light and heat act as powerful accelerants in this process.